That is well and good—perhaps this Kat does not really understand the underlying context of joint development. But what happens when the circumstances hit much closer to home? In particular, what happens when there are joint authors of a chapter of a legal text and one of the joint authors discontinues his involvement in the project, but the updated text continues to contain content to which the erstwhile joint author has contributed? Given the time and research requirements, acceptance of this responsibility sometimes leads to a situation where there are co-authors of the chapter, and the co-authorship goes on for year to year (I shall pass over the tawdry possibility that senior partner X will instruct young associate Y to do most of the work, but Y's contribution is relegated, at best, to a brief comment in a footnote—"X thanks Y for his or her contribution in the preparation of this chapter.") It is assumed that the publisher will sort out the copyright ownership issue, either by licence or assignment. The issue is therefore not one of "co-ownership" per se, but co-authorship and the right of attribution: does the erstwhile author continue to have the right to be identified as a co-author, for as long as content that he has created is part of the updated contents (subject perhaps to a reservation such as—"Y was a co-author of this chapter until 2013")?
Under the basic principle of moral rights, an author has the right to be credited for the work—but not in all jurisdictions and not for all works. Most notably, in the U.S under federal law, moral rights apply explicitly only to works of visual art under the Visual Artists Rights Act, here. In many other jurisdictions, the attribution right applies broadly to all types of protected works. Against that backdrop, consider a contractual provision, drafted under an applicable U.S. state law, which provides that "the publisher may, but is not obligated, to continue to identify the co-author for as long as his contents are included in the updated chapter." Ab initio, the prospective co-author may seek to negotiate the provision so as to impose an obligation on the publisher, and the bargaining strength of the parties will determine the success of such an attempt.
Apart from issues of contract law and copyright/moral rights law, this Kat wonders why a publisher would choose to submerge the identity of the erstwhile co-author. Perhaps the relationship between the co-authors is such that the remaining co-author will not continue with the project if the erstwhile co-author continues to be identified. Perhaps the publisher has marketing and promotional reasons to submerge the identity. Given, however, the basic expectation of any author to be identified with his work, this Kat finds it most curious that some publishers apparently will go to substantial lengths to reserve the right to withhold identification under certain circumstances. Whatever the reason, the situations in which the former co-author of an updated book chapter may not be identified by the publisher in a subsequent update suggests how the challenges of co-ownership can be transmogrified into the problem of co-authorship in the copyright/moral rights context.